1. Field of the Invention
The present invention is directed to an implantable cardiac defibrillator, and in particular to an electrode arrangement for such a defibrillator.
2. Description of the Prior Art
Implantable defibrillators are known in the art as disclosed, for example in U.S. Pat. No. 4,030,509 which consists of a defibrillator housing, in which the defibrillation power source and defibrillation processing circuitry are contained, and an electrode connected to the housing via an electrode line for supplying defibrillation therapy, in the form of electrical energy, to the heart. Known electrode arrangements are planar, and are adapted for application against the exterior of the heart so as to be able, insofar as possible, to depolarize all excitable cells of the heart in the event of a cardiac arrhythmia, such as fibrillation, by delivering an output in the form of a current surge from the housing via the electrode line.
In order to initiate and control defibrillation, it is necessary to monitor the functioning of the heart so as to be able to detect, inter alia, tachycardia and/or ventricular flutter. In conventional defibrillators, this is undertaken by intracardial acquisition of selected physiologic parameters in the right side of the heart. In a defibrillator disclosed by European application 0 009 255, for example, a catheter having, inter alia, sensor electrodes is placed in the right side of the heart by which an intracardial ECG is acquired, as well as a signal corresponding to the mechanical pumping action of the heart, obtained indirectly by an impedance measurement.
A cardioverter is disclosed in U.S. Pat. No. 3,942,536 wherein a stimulation catheter is placed in the right side of the heart, which includes a pressure sensor for monitoring the heart function.
A cardioverter is disclosed in U.S. Pat. No. 3,805,795 having a catheter with electrodes for acquiring an ECG and also a sensor for monitoring the muscle contractions of the heart. The sensor consists of an elastic, plastic member having carbon particles embedded therein, the contact resistance of these carbon particles changing upon motion or distortion of the sensor, so that muscle contractions of the heart can be monitored by measuring the overall resistance of the plastic member.
Because the introduction of intracardial sensors can be undertaken without difficulty only in the right side of the heart, no direct monitoring of the functioning of the left side of the heart can be undertaken with such known sensor catheters.
A heart pacemaker having one or more detectors for monitoring heart noises, is disclosed in U.S. Pat. No. 4,763,646, the detectors being in the form of a microphone, a pressure sensor or an acceleration sensor, and the detectors being optionally arranged in an electrode lead of the pacemaker, within the heart pacemaker housing, or outside the heart pacemaker housing connected thereto via a separate lead. This patent discloses placement of the sensors in the proximity of the heart, however, the arrangement of the detectors outside of the heart is not defined so that, for example, a discrimination between heart signals from the right side of the heart and signals from the left side of the heart is not possible without further steps being undertaken, and it is also possible that signals due to other body functions could be superimposed on the signals which are intended to be detected.